The proposed program of experimentation focuses on the process of word-learning and the subsequent mental representation of the new word in non-fluent aphasics, fluent aphasics, non-aphasic patients with right hemispheric insult, and normal adults. The acquisition of grammatical and referential aspects of new content words, and the use of functors to infer properties of new words will be carefully assessed after localized cerebral insult by experiments featuring multiple probes for lexical knowledge of new and known (control) words. The first series of studies examines the subject's knowledge of contentives. Various types of words will be assessed: A new color term; a know color term which cannot be retrieved; a verb with a variety of grammatical constraints; and a noun with a rich internal semantic structure. The multiple probes of each experiment will concentrate on a specific aspect of the contentive which figures prominently in the mental lexicon; a common battery of tasks will allow some comparisons between words. The second series of studies assesses the patient's ability to make inferences about new words on the basis of his knowledge of functors. We evaluate the appreciation of an article for purposes of differentiating, first, between a proper noun and a common noun and, second, between a noun phrase and a verb phrase; we assess the patient's capacity to determine the appropriate real world context within which to apply his knowledge of functors; and we examine the patient's ability to discriminate among closely related grammatical sub-categories. These data will allow us to describe lexical processing after circumscribed cerebral lesions, to constrain further psycholinguistic theories, and to secure pivotal observations for remedial language therapy.